1. Field of the Invention
The present invention relates to a pump system having hydraulic pump bodies arranged in parallel, a charge relief mechanism and an oil pressure control mechanism.
2. Related Art
A pump system comprising a plurality of hydraulic pump bodies arranged in parallel with respect to each other, and forming a transmission path in cooperation with a hydraulic actuator such as a hydraulic motor unit arranged spaced apart from and fluidly connected with the pump system, has been used in various fields of a travel transmission mechanism of a working vehicle and the like (see, for example, U.S. Pat. No. 6,425,244).
Specifically, such a conventional pump system includes a plurality of hydraulic pump bodies arranged in parallel, a plurality of pump shafts respectively driving the plurality of hydraulic pump bodies, a power transmission mechanism for operatively connecting the plurality of pump shafts with respect to each other, and a pump case for accommodating the plurality of hydraulic pump bodies and the power transmission mechanism and, also, supporting the plurality of pump shafts in a rotatable manner about an axis line.
The pump case has a center section (or port block), with which the plurality of hydraulic pump bodies are brought into contact in a rotabable manner. The port block forms a supply/discharge oil passage for the plurality of hydraulic pump bodies therein.
One of the pump shafts of the plurality of pump shafts has one end which is supported to the pump case so as to extend outward and is operatively connected to a driving source via a transmission mechanism such as a pulley.
The conventional pump system has a possibility that a sliding face of one hydraulic pump body driven by one pump shaft is tilt with respect to an inner surface (a face facing the hydraulic pump body) of the port block.
In other words, a force in a direction orthogonal to an axis line direction is applied to the one pump shaft operatively connected to the driving source via the pulley or the like.
That is, the force orthogonal to the axis line direction is constantly applied to the one pump shaft, thereby causing this pump shaft to deflect.
The deflection of the one pump shaft causes an operating oil leak between the hydraulic pump body (hereinafter, referred to as one hydraulic pump body) driven by the one pump shaft and the port block, thus lowering transmission efficiency.
Further, in the case of using the conventional pump system as a travel transmission mechanism of a vehicle, the straight advancement of the vehicle degrades due to the operating oil leak.
That is, since the force in the orthogonal direction as described above does not act on the pump shafts other than the one pump shaft, the operating oil leak does not occur at the other hydraulic pump bodies (hereinafter, referred to as the other hydraulic pump bodies) driven by the other pump shafts.
Therefore, even when the hydraulic pump bodies are operated so that oil supply/discharge rates of the one hydraulic pump body and the other hydraulic pump bodies are the same to advance the vehicle straightly, the oil supply/discharge rates will differ due to the operating oil leak from the one hydraulic pump body, thus worsening the straight advancement of the vehicle.
The present invention has been made in view of the prior art, and one object of the present invention is to provide a pump system having a plurality of hydraulic pump bodies arranged in parallel and a plurality of pump shafts respectively driving the plurality of hydraulic pump bodies, and capable of preventing an operating oil leak from the hydraulic pump body driven by one pump shaft operatively connected to a driving source as much as possible.